1. Field of the Invention
The present invention relates to an integrated circuit such as a D/A-converter-built-in LSI with analog and digital elements mixed therein and, more particularly, to a D/A converter-built-in integrated circuit that allows ease testing its D/A converter section.
2. Description of the Prior Art
FIG. 10 illustrates in block form the configuration of a conventional D/A-converter-built-in LSI with analog and digital elements mixed therein. The LSI identified generally by 1 has a logic/RAM circuit 2, a clock/timing generator 3 for generating an internal clock of the LSI 1 and an 8-bit D/A converter (hereinafter abbreviated as a DAC) 4. The clock/timing generator 3 supplies the logic/RAM circuit 2 with a clock and the DAC 4 with a timing signal for D/A conversion. The LSI 1 has a large number of input terminals 5 and an analog output terminal 6.
In testing of the DAC 4 of the LSI 1, data is input via the digital I/O terminals 5 so that the DAC 4 outputs a signal of triangular or sawtooth waveform, and the waveform of the output signal from the analog output terminal 6 is converted from analog to digital form, thereafter being subjected to digital arithmetic processing to present test conclusions.
In Japanese Pat. Laid-Open Gazette No. 360418/92, there is disclosed a configuration in which either one of a digital input and the output from a synchronous counter having counted pulses generated by a pulse generator is selectively input into a digital-to-analog converter under the control of a linearity measurement control signal input to test it. In Japanese Pat. Laid-Open Gazette No. 45935/94 there is proposed a scheme of testing a D/A converter by selectively applying thereto either one of the output from a digital circuit and the output from a counter circuit. Similar techniques are disclosed in Japanese Pat. Laid-Open Gazettes Nos. 258402/94 and 152412/94 as well. With the apparatus disclosed in these gazettes, however, the linearity hysteresis cannot be tested because the counter used operates only in one direction; therefore, no accurate linearity test can be made.
The integrated circuit with a built-in D/A converter has such a construction as mentioned above, and hence it needs to be supplied with a relatively complex signal via a digital input terminal--this gives rise to a problem that the testing apparatus itself is inevitably complex and expensive. Additionally, it is difficult to conduct the hysteresis test with ease.